I totally get that instructions in a CONTRIBUTING file can be daunting. Surely some are much more terse than others.
But where to draw the line? How much knowledge should this, or any other technical documentation, assume?
When documenting a project’s API, the writer must write to an audience. If there’s no baseline, documentation will overreach and become harder to use. When writing developer docs, the baseline is somewhat higher.
You may want to consider that there’s probably better documentation on how to use Gulp on Gulp’s site, instead of whatever a user of Gulp would write in CONTRIBUTING.
For the collaborator writing contribution instructions, maybe linking to resources — such as Gulp’s site — would strike a good balance.